Freeze tape casting systems and methods

Abstract

A freeze tape casting system is provided that maximizes the production speed of a tape material with a directional porosity through a thickness of the tape material. Embodiments of the system may have multiple freeze zones where a freeze zone has a temperature profile and dwell time that is tailored to one or more parts of the physical process of freezing a solvent in the tape material to create the directional porosity. Various zones can be directed to physical processes such as nucleation, transitional crystal growth, steady crystal growth, maintaining the tape material in a frozen state, sublimating the frozen solvent, etc. As a result, the physical processes are decoupled from each other to maximize production speed. The resulting material has applicability in electrodes, current collectors, and other products.

We claim: 
     
         1 . A freeze tape casting system, comprising:
 a carrier film moving in a production direction;   a slurry having a solvent, the slurry deposited onto the moving carrier film to form a tape material;   a nucleation zone extending a first distance along the production direction, and the nucleation zone providing a nucleation temperature profile beneath the carrier film to initiate nucleation of the solvent from a liquid phase to a solid phase at a plurality of discrete locations in the tape material; and   a steady growth zone extending a second distance along the production direction and positioned after the nucleation zone in the production direction, and the steady growth zone providing a steady growth temperature profile beneath the carrier film to continue freezing of the solvent from at least one of the plurality of discrete locations in a growth direction through a thickness of the tape material, wherein the nucleation temperature profile is distinct from the steady growth temperature profile, and the first distance is distinct from the second distance.   
     
     
         2 . The freeze tape casting system of  claim 1 , further comprising:
 a transition zone extending a third distance along the production direction and positioned between the nucleation zone and the steady growth zone along the production direction, and the transition zone having a transition temperature profile to promote freezing of the solvent from at least one of the plurality of discrete locations in the growth direction over other directions, wherein the transition temperature profile is distinct from the nucleation temperature profile and distinct from the steady growth temperature profile, and the third distance is distinct from the first distance and distinct from the second distance.   
     
     
         3 . The freeze tape casting system of  claim 1 , further comprising:
 a cooling system positioned beneath the carrier film in the nucleation zone, wherein the cooling system generates the nucleation temperature profile.   
     
     
         4 . The freeze tape casting system of  claim 3 , wherein the cooling system comprises a pump that moves a coolant fluid through a loop. 
     
     
         5 . The freeze tape casting system of  claim 3 , wherein the cooling system comprises a plurality of thermoelectric coolers. 
     
     
         6 . The freeze tape casting system of  claim 1 , wherein the solvent is water, and the nucleation temperature profile is between −2 and −150 degrees Celsius. 
     
     
         7 . The freeze tape casting system of  claim 1 , wherein the solvent is water, and the steady growth temperature profile is between 0 and −60 degrees Celsius. 
     
     
         8 . The freeze tape casting system of  claim 1 , wherein the nucleation temperature profile varies along the first distance in the production direction. 
     
     
         9 . A method for forming pores in a tape material, comprising:
 moving a carrier film in a production direction;   depositing a slurry onto the carrier film at a predetermined thickness to form a tape material having a solvent;   initiating nucleation of the solvent from a liquid phase to a solid phase at a plurality of discrete locations in the tape material by moving the carrier film and the tape material through a nucleation zone having a nucleation heat flux applied by a first cooling component;   freezing the solvent from at least one of the plurality of discrete locations in a growth direction through the thickness of the tape material by moving the carrier film and the tape material through a steady growth zone having a steady growth heat flux applied by a second cooling component, wherein the applied steady growth heat flux is different from the applied nucleation heat flux; and   removing the solvent from the tape material to leave pores oriented along the growth direction in the tape material.   
     
     
         10 . The method of  claim 9 , wherein frozen solvent is removed from the tape material by sublimation. 
     
     
         11 . The method of  claim 9 , further comprising:
 detecting, by a temperature sensor, a temperature of the nucleation zone used to determine an initial nucleation heat flux;   determining, by a control unit, a final nucleation heat flux based on the solvent of the tape material and the thickness of the tape material; and   causing, by the control unit, a cooling system to change the initial nucleation heat flux to the final nucleation heat flux.   
     
     
         12 . The method of  claim 9 , further comprising:
 providing at least one roller in operable communication with a control unit, wherein the at least one roller is connected to the carrier film to move the carrier film in the production direction;   receiving, by the control unit, an initial rotation speed of the at least one roller;   determining, by the control unit, a final rotation speed of the at least one roller such that the carrier film moves at a predetermine rate, and a given point of the tape material moves through the nucleation zone for a nucleation dwell time and moves through the steady growth zone for a steady growth dwell time; and   causing, by the control unit, the at least one roller to change the initial rotation speed to the final rotation speed.   
     
     
         13 . The method of  claim 9 , further comprising:
 detecting, by a temperature sensor, an initial temperature of an ambient gas above the carrier film and the tape material;   determining, by a control unit, a final temperature based on the solvent of the tape material and the thickness of the tape material; and   causing, by the control unit, an ambient control unit to change the initial temperature to the final temperature and establish the nucleation heat flux through the thickness of the tape material in the nucleation zone and the steady growth heat flux through the tape material in the steady growth zone.   
     
     
         14 . A freeze tape casting system, comprising:
 a control unit programmed to independently control a temperature profile of a first zone and a temperature profile of a second zone;   a first temperature sensor in operable communication with the control unit, the first temperature sensor detects a temperature that is part of an initial first temperature profile in the first zone;   a second temperature sensor in operable communication with the control unit, the second temperature sensor detects a temperature that is part of an initial second temperature profile in the second zone;   a cooling system in operable communication with the control unit, the cooling system positioned beneath a carrier film in the first and second zones;   instructions that, when executed by the control unit, cause the control unit to:
 receive the temperature that is part of the initial first temperature profile in the first zone; 
 determine a final first temperature profile based on a solvent in a tape material on the carrier film; 
 cause the cooling system to change the initial first temperature profile to the final first temperature profile in the first zone; 
 receive the temperature that is part of the initial second temperature profile in the second zone; 
 determine a final second temperature profile based on the solvent in the tape material on the carrier film; 
 cause the cooling system to change the initial second temperature profile to the final second temperature profile in the second zone. 
   
     
     
         15 . The freeze tape casting system of  claim 14 , wherein the cooling system comprises a first coolant loop positioned beneath the carrier film in the first zone and a second coolant loop positioned beneath the carrier film in the second zone. 
     
     
         16 . The freeze tape casting system of  claim 14 , wherein the first zone is a nucleation zone, and the final first temperature profile initiates nucleation of the solvent from a liquid phase to a solid phase at a plurality of discrete locations in the tape material, wherein the second zone is a steady growth zone, and the final second temperature profile continues freezing of the solvent from at least one of the plurality of discrete locations in a growth direction through a thickness of the tape material. 
     
     
         17 . The freeze tape casting system of  claim 14 , further comprising:
 an ambient temperature sensor in operable communication with the control unit; the ambient temperature sensor detects an initial ambient temperature of an ambient gas above the carrier film and the tape material;   an ambient control unit in operable communication with the control unit, the ambient control unit positioned above the carrier film and the tape material;   instructions that, when executed, cause the control unit to:
 receive the initial ambient temperature from the ambient temperature sensor; 
 determine a final ambient temperature based on the solvent in the tape material on the carrier film; 
 cause the ambient control unit to change the initial ambient temperature of the ambient gas to the final ambient temperature of the ambient gas and establish a first temperature gradient through the thickness of the tape material in the first zone and a second temperature gradient through the tape material in the second. 
   
     
     
         18 . The freeze tape casting system of  claim 14 , wherein the control unit determines the initial first temperature profile. 
     
     
         19 . The freeze tape casting system of  claim 14 , further comprising:
 at least one roller in operable communication with the control unit, wherein the at least one roller is connected to the carrier film to move the carrier film in a production direction;   instructions that, when executed, cause the control unit to:
 receive an initial roller speed from the at least one roller; 
 determine a final roller speed based on the solvent in the tape material on the carrier film; 
 cause the at least one roller to change the initial roller speed to the final roller speed. 
   
     
     
         20 . The freeze tape casting system of  claim 14 , further comprising:
 instructions that, when executed, cause the control unit to:
 receive the final first temperature profile; 
 determine a dwell time for the tape material in the first zone; 
 cause the cooling system to change an axial length of the first zone along a production direction.